Among biodegradable resins, a polylactic acid resin is inexpensive because L-lactic acid used as a raw material is produced by a fermentation method using a sugar extracted from maize, potatoes, or the like. Also, the polylactic acid resin has a very low amount of a total carbon oxide discharge because the raw material is plant-derived, and the properties of the resin include strong rigidity and high transparency. Therefore, the utilization of polylactic acid resins is expected to be promising at present.
However, in addition to the properties mentioned above, since polylactic acid resin also has the properties of being brittle and hard, and lacking flexibility, its applications are limited, so that there are hardly any practical achievements in the fields of daily sundries, household electric appliance parts, automobile parts, and the like. In addition, when the resin is molded into an injection molded article or the like, there are some disadvantages such as mechanical strength such as flexibility or impact resistance is insufficient, and whitening upon bending or worsening of hinge properties takes place, so that the resin is not used at present.
In addition, the polylactic acid resin has a delayed crystallization velocity, and has an amorphous state after being injection-molded, so long as a mechanical processing such as stretching is not carried out. The polylactic acid resin has a low glass transition temperature (Tg) of 60° C., so that there is a disadvantage that the resin cannot be used under an environment condition of a temperature of 55° C. or higher.
Further, in order to utilize the polylactic acid resin in durable materials such as household electric appliance parts or automobile parts, aside from being provided with heat resistance and mechanical strength, the polylactic acid resin having a certain level of flexibility is in demand.
On the other hand, as a technique of applying a polylactic acid resin in hard field, various proposals of adding a reinforcing material have been made (see, for example, JP-A-2005-23250, JP-A-2007-100068, and WO 2007/015371).